Air Tightness & KISS

To "Keep It Simple Stupid" does make sense for some air tight details at the building envelope too.

The photo beside was found recently in a specialist magazine for insulation, air tightness, building service, ventilation and green materials.

Beside the fact that I can´t see the reason for using expanding foam on top, there´s nothing wrong regarding the air tight performance of this detail.

You can do it by using tapes, membranes and foam but not necessarily.

As you might can see, the joists are not going into the wall - they´ve been fixed on top with joist hangers. That means, there has to be no air infiltration
expected from the cavity wall. The aim is only, to make the block work around the joists air tight.

The faster, cheaper, easier (or simple: just better) solution would be, to use an air tight paint and coat the particular area before installing the joists.
KISS!